This invention relates to a runner chopper.
When plastic products are manufactured by injection molding, runners of the plastic material are produced as a by-product.
A runner is a piece of plastic that is hardened in a channel or region connecting a nozzle of the injection molding machine with one of several cavities formed in a metal mold.
The plastic material in the runners can be reused by collecting the runners and supplying them to a crusher where they are broken into fine particles of plastic. Thus, the standard one-step crushing method converts runners directly into reusable plastic materials.
Though runners take various shapes according to the arrangement of cavities in a metal mold, they are normally long and bulky.
Because the elongate runners are fed directly into the crusher, the entrance to the crusher must be wide enough and the crusher must be long enough to accommodate them.
Moreover, because the crusher must smash the runners directly into fine particles, the blades of the crusher are rotated at high speed.
In the crusher a plurality of rotary blades are fitted around a main shaft which is rotated within a cylindrical casing of the crusher.
In a conventional crusher the plurality of rotary blades are fixed on the shaft without relative gaps between neighboring blades, and the gap between the casing and the blades is very narrow.
The runners are crushed and ground into fine particles in the narrow gap between the outer surfaces of the rotary blades and the inner surface of the casing by the shearing stresses generated by the rotation of the rotary blades. Thus the outer surface of the rotary blades provides the crushing force.
In order to rapidly crush the runners into fine particles, the rotary blades must be driven at high speed. Consequently, the crusher requires a substantial driving horsepower to overcome the large shear stresses and provide the high rotational speed.
In conventional runner crushers, the rotational speed is generally more than a thousand revolutions per minute and the driving power is between five to ten horsepower.
Unfortunuately, the conventional runner crushers are extremely noisy and produce large vibrations because of the high rotational speed and the necessary high driving force. These noises and vibrations are undesirable because they pollute the working environment and distress the worker.
Furthermore when a plastic molding machine is driven automatically overnight, plastic runners are conveyed into the runner crusher. The loud noise of the operating crusher becomes an incessant nuisance to neighbors, particularly at night. Consequently, it is desirable to suppress these nocturnal noises.